This invention is concerned with a manipulator for positioning a series of workpieces relative to an industrial robot by means of which the workpieces, one after the other, are to be processed, said manipulator comprising at least two separate fixture supports transferable between a loading position, in which exchange of workpieces in fixtures carried by the fixture supports may take place also during the operation of the robot, and an operative position, in which the workpiece mounted in the respective fixture support is held within the operating range of the robot and is rotatable about an axis, the position of which relative to the robot is predetermined, such transfer being effected by means of a turning motor which is co-ordinated with the operational movements of the robot through a control system in order to render various surface portions and parts of the workpiece accessible to an implement handled by the robot. This implement may for example be a welding gun, by means of which parts incorporated in a workpiece are to be welded together, or a spray gun, by means of which a workpiece is to be surface treated.
Manipulators of the kind just defined, which have been known for a long time, offer many advantages such as that the robot does not need to be moved during its operation and may be utilized to an optimum extent. However, they also have certain drawbacks, namely a fairly complex construction and, hence, they are expensive to manufacture. One of the reasons for this is that in the manipulators so far known the various fixture supports have always been provided with their own separate turning motors. These turning motors, which under the influence of remote control signals must be capable of changing the angular positions of the fixture supports relative to the robot with high accuracy, are in themselves expensive and require in addition fairly complex electrical coupling arrangements in order to be alternately co-ordinated with the robot. In the known manipulators there was also a need for special means for keeping the fixture supports in correct working position during the operation of the robot, and the handling of elongate workpieces frequently presented considerable difficulties.